Fabrication of plastic spinnerettes by means of stacked mandrels

ABSTRACT

The disclosed molding apparatus includes a plurality of mandrels, each in the form of a comb having spaced, parallel teeth, assembled into a mandrel stack. The mandrel stack is supported above a mold cavity into which the teeth extend. A plastic resin is poured into the mold and cured, and the mandrel stack is separated from the mold cavity to withdraw the teeth uniformly from the resulting casting. The holes left in one surface of the casting are filled with a grouting material, and the casting machined to form a finished spinnerette having shaped orifices.

United States Patent Murfitt et al.

[ 1 Aug. 29, 1972 [54] FABRICATION OF PLASTIC SPINNERETTES BY MEANS OFSTACKED MANDRELS [72] Inventors: Donald Murfitt; James Bruce Peeso,

Jr., both of Stamford, Conn.

[73] Assignee: American Cyanamid Company,

Stamford, Conn.

[22] Filed: Dec. 15, 1969 [2]] Appl. No.: 889,794

Related US. Application Data [62] Division of Ser. No. 723,696, April24, 1968,

abandoned.

[52] US. Cl. ..249/160, 264/225, 425/186 [51] Int. Cl. ..D01d 3/00 [58]Field of Search....l8/8 SS, 8 R, 8 WB, 8 SM, 34, 18/42 D, 44; 249/124,125, 160; 264/225,

[56] References Cited v UNITED STATES PATENTS Mayer et al ..18/42 D2,797,442 7/1957 Wagner ..249/l25 X 3,226,771 l/l966 Szugda 1 8/42 D3,312,583 4/1967 Rochlis ..l8/D1G. 8 3,551,936 l/l97l Kutik et al...l8/DlG 8 3,357,058 12/1967 Kutik ..18/D1G. 8

Primary Examiner-4. Spencer Overholser Assistant Examiner-Lucius R. FryeAttorney-Philip Mintz 5 7 ABSTRACT The disclosed molding apparatusincludes a plurality of mandrels, each in the form of a comb havingspaced, parallel teeth, assembled into a mandrel stack. The mandrelstack is supported above a mold cavity into which the teeth extend. Aplastic resin is poured into the mold and cured, and the mandrel stackis separated from the mold cavity to withdraw the teeth uniformly fromthe resulting casting. The holes left in one surface of the casting arefilled with a grouting material, and the casting machined to form afinished spinnerette having shaped orifices.

9 Claims, 12 Drawing figures Patented Aug. 29, 1972 4 Sheets-Sheet l Nmy I INVENTORS DONALD MURF/TT JAMES enuc: PEESO, JR.

ATTORNEY I Patented Aug. 29, 1972.

I Q 4 Sheets-Sheet 2 MUM ' INVENTORSV A r TORNEX Patented Aug. 29, 19723,687,413

4 Sheets- Sheet 5 2 V 95a 95a INVENTORS DONALD MURF/TT JAMES BRUCEPEESO, JR.

A r TORNE Y Patented Aug. 29, 1972 3,687,413

I I v v I 4 Sheets-Sheet 4.

I INVENTORS J 15.5 DONALD MURF/TT BY JAMES BRUCE PE E 50, JR.

A TTORNE Y FABRICATION F PLASTIC SPINNERETTES B MEANS OF STACKEDMANDRELS This is a division of application Ser. No. 723,696, filed Apr.24, 1968, now abandoned.

BACKGROUND OF THE INVENTION Spinnerettes used in the production ofvarious synthetic fibers have been made in various ways down through theyears. The most difficult and expensive aspect of manufacturingspinnerettes lies in the formation of a multitude of extrusion orificestherein; the number os such orifices ranging in the thousands for someapplications. Typically, these spinnerette orifices have been formed bypunching or drilling holes in a metal sheet or cup. This is an expensiveprocess, costing as much as 25 cents per hole, particularly when largenumbers of closely spaced spinnerette orifices are required.

Recently, attention has been given to the use of plastics and glass as aspinnerette material. Plastic spinnerettes formed of epoxy resin forexample, have been found to be particularly useful in the manufacture ofshaped synthetic fibers by a wet spinning process. The poor thermalconductivity of the plastic reduces heat losses from the hot dope behindthe spinnerette to the cold coagulant and thus assists in themaintenance of more uniform dope temperatures. More uniform dope flowrates at the spinnerette orifices are therefore achieved. In thecopending application of Story and Bundegaard, Ser. No. 696,495, filedJan. 9, 1968 and assigned to the assignee of the instant application, aprocess is described for spinning acrylic synthetic fibers ofrectangular cross-section using plastic spinnerettes.

Various methods have been suggested for producing plastic spinnerettes.For example, in U. S. Pat. 2,623,241, a process is disclosed wherein aplastic is cast about a network of parallel wire filaments. After thecasting is cured, the wire filaments are removed by an acid etchsolution to produce spinnerette orifices. It will be appreciated thatthis manufacturing technique suffers from the distinct disadvantage thatthe most significant element of the casting apparatus, namely, the wirefilaments, is destroyed in the production of each spinnerette.Consequently, it is virtually impossible to produce two identicalspinnerettes by this process. In

other words, it would be virtually impossible to obtain two spinneretteshaving identical orifice patterns. This lack of reproducibility is adistinct drawback particularly when concerned with spinning high qualitysynthetic fibers. Moreover, this technique is expensive and timeconsuming since the casting apparatus must be effectively reconstructedprior to the casting of each spinnerette.

SUMMARY OF THE INVENTION According to the present invention there isprovided an improved method for producing spinnerettes employing novelcasting apparatus. The method of the invention provides for themanufacture of a plurality of spinnerettes from the same castingapparatus. In other words, once the casting apparatus of the presentinvention is assembled, it is usable to produce a plurality ofspinnerettes in succession. As a consequence, each of the spinnerettesso formed has identical spinnerette orifice dimensions and spacing.Moreover, the orifices in any one spinnerette are of uniform dimensions.The apparatus of the invention is particularly suited for formingspinnerettes having shaped orifices, and particularly orifices havingrectangular cross-sections. The apparatus is however conducive toforming spinnerettes having various orifice configurations anddimensions.

The method of the present invention may be carried out expeditiously berelatively unskilled personnel. Quantity production of spinnerettes isachieved at a fraction of the cost of manufacture by prior arttechniques. The casting apparatus of the invention, once assembled, needbe only partially disassembled pursuant to each casting operation. Theapparatus is in no way impaired or destroyed incident to a castingoperation. In the event of inadvertent damage to a forming element ofthe casting apparatus, the apparatus may be disassembled and the damagedelement replaced.

According to the method of the present invention, a mold is formedhaving a plurality of mandrel elements extending into a mold cavity. Acastable material, such as an epoxy resin, is poured into the moldcavity such that the distal ends of the mandrel elements are submergedtherein. After the resulting casting has hardened, the mandrel elementsare withdrawn leaving a plurality of blind holes therein. The casting isremoved from the mold and machined to the form and dimensions of afinished spinnerette with the holes becoming spinnerette orifices.

It is preferred that the holes formed in the casting be filled with agrouting material prior to grinding. Once the casting has been machined,the grouting material is then removed from the orifices. A mountingflange and reinforcing ribs may then be bonded to the spinnerette.

The casting apparatus includes a plurality of comblike mandrels, eachhaving a plurality of tooth-like elements extending in a commondirection in parallel, spaced relation. The mandrels and mandrel spacersare assembled together to form a mandrel stack which is supported abovethe mold cavity. A jack mechanism, also included in the mandrel stackfacilitates substantially uniform withdrawal of the mandrel teeth enmasse from the spinnerette casting.

The mandrels are formed having a supporting strip or backbone with thetoothlike elements or teeth joined thereto along one edge such as toextend generally in the same direction in parallel, spaced relation. Thebackbone of each mandrel is provided with means for aligning andmounting it in a mandrel stack assembly. All mandrels are of identicalconstruction and may readily be replaced in the mandrel stack should theteeth break off or the mandrel otherwise damaged.

The invention accordingly comprises the several steps and the relationof one or the other of such steps with respect to each of the others andthe apparatus embodying features of construction, combinations ofelements and arrangements of parts which are adapted to effect suchsteps, all as exemplified in the following detailed description, and thescope of the invention will be indicated in the claims.

For a fuller understanding of the nature of the invention, referenceshould be had to the following detailed description taken in connectionwith the accompanying drawing, in which:

FIG. 1 is a perspective view of a molding apparatus constructedaccording to one embodiment of the invention for producing circularspinnerettes;

FIG. 2 is a side elevational, sectional view of the molding apparatus ofFIG. 1;

FIG. 3 is a side elevational view of one of the mandrels used in theapparatus of FIG. 1;

FIG. 4 is a side elevational view of a mandrel spacer used in theapparatus of FIG. 1;

FIG. 5 is a perspective view of a jack spacer and a thrust bar used inthe apparatus of FIG. 1;

' FIG. 6 is a perspective view of a spinnerette plate produced using theapparatus of FIG. 1;

FIG. 7 is a perspective view of the spinnerette plate of FIG. 6 adaptedwith a mounting flange and reinforcing ribs;

. drel spacer used in the apparatus of FIGS. 8 and 9; and

FIG. 12 is a side elevational view of another form of mandrel spaceremployed in the apparatus of FIGS. 8 and 9.

Like reference numerals refer to like parts throughout the several viewsof the drawings.

DETAILED DESCRIPTION OF THE INVENTION According to one embodiment of theinvention, a spinnerette casting apparatus, generally indicated at inFIGS. 1 and 2, includes a mandrel stack assembly, generally indicated at22, supported on a cavity mold assembly, generally indicated at 24. Thecavity mold assembly 24 is comprised of three plate sections 25, 26, and27 secured together in sandwich relation by bolts 28. As best seen inFIG. 2, the upper and middle plate sections and 26, respectively, arecentrally apertured so as to define a casting mold cavity 30 forcontaining a castable material 31, such as epoxy resin. A suitable resinis Eccobond 55, supplied by Emerson & Cumming, Inc. However, it isunderstood that a wide variety of castable materials will occur to thoseskilled in the art, and the instant invention is not to be deemedlimited to any particular one or type.

The castable resin 31 contained in cavity 30 is introduced through apour hole 32 in the top plate section 25. Pour hole 32 communicates withone end of a slot 33 in middle plate section 26, the slot opening intocavity 30. For purposes of illustration, the pour hole 32 and slot 33are shown out of their true positions in FIG. 2. The bottom platesection 27 is formed having a circular recess 35 for receiving a core36, which is secured in place by bolts 37. Since the core 36 is usedmainly to conserve casting resin it may be omitted without departingfrom the invention.

Still referring to FIGS. 1 and 2, the mandrel stack 22 includes aplurality of comb-like mandrels alternating with mandrel spacers 42.Each mandrel, as best seen in FIG. 3, comprises a supporting strip orbackbone 40a carrying a plurality of teeth 40b distributed along oneedge thereof. The teeth lie in the plane of the backbone 40a and dependtherefrom in parallel, spaced relation. Holes 40c, formed in thebackbone 40a, facilitate alignment and assembly of the individualmandrels 40' in the mandrel stack 22, as will be described.

The mandrels 40 are preferably formed by photoetching from thin stripsof a suitable metal such as beryllium copper alloy. However, it will beappreciated that the mandrels 40 need not be formed from a strip as theteeth 40b may be butt-welded or otherwise secured along one edge of thebackbone 40a. Other ways of forming the mandrels 40 will occur to thoseskilled in the art.

The thickness of the backbone 40a and teeth 40b may vary depending onthe dimensional characteristics of the spinnerette to be formed, buttypically is less than 0.04 inches. Exemplary mandrel dimensions may be0.003 inch for the thickness of the backbone and teeth, 0.015 inch forthe width of each tooth, and 0.073 inch spacing between teeth. Eachmandrel may have any number of teeth. The mandrel teeth need not be ofuniform size along their lengths, but may be tapered down at theirdistal ends. As will be appreciated, their distal ends cannot, however,be larger in size than their proximal ends. While the mandrel teeth areshown to be rectangular in crosssection, thus forming spinneretteorifices for spinning ribbon-shaped fibers, it will be appreciated thatthe mandrel teeth may be of any desired cross-section. Moreover, thethickness of the backbone 40a need not correspond to the thickness ofthe teeth 40b. If the backbone is made thicker than the teeth, themandrel spacers 42 could be omitted from the mandrel stack 22.

Each of the mandrel spacers 42, best seen in FIG. 4, is formed of asuitable metal such as copper and has length and width dimensionscorresponding to the mandrel backbones 40a. The thickness of the spacersis determined by the spacing desired between the teeth of adjacentmandrels. Holes 42a in the mandrel spacers are provided for purposes ofaligning and assembling them in alternating relation with the mandrels40 in the mandrel stack 22.

Returning to FIGS. 1 and 2, the mandrels 40 and mandrel spacers 42 arethreaded onto a pair of elongated clamp rods 46 which extend through theholes 40c in the mandrels and the holes 420 in the mandrel spacers. Theends of the clamp rod 46 extend through bores in opposing clamp blocks48. Nuts 50 threaded on the ends of the clamp rods 46 serve to clamp themandrels 40 and mandrel spacers 42 between clamp blocks 48.

Also included in the mandrel stack 22 are a plurality of jack spacers,generally indicated at 52, whose function is to assist in withdrawal ofthe mandrel stack from the cavity mold 24, as will be described. Thejack spacers 52, inserted at spaced intervals in the mandrel stack 22,are each constructed in the manner shown in FIG. 5. Thus,'each jackspacer 52 includes an elongated bar 52a of rectangular cross-sectionhaving transverse holes 52b for receipt of the clamp rods 46 uponassembly into the mandrel stack 22. A plurality of jack screws 52c areaccommodated in threaded bores in the bar 52a. These threaded boresextend in a direction transverse to the holes 52b such that the jackscrews 520 are vertically oriented when the jack spacers are assembledin the mandrel stack 22.

Included with each jack spacer 52 in the mandrel stack 22 is a thrustbar 54, one of which is stationed immediately beneath each jack spacer(FIG. 5). The extremities of the thrust bars 54 are supported on the topsurface of the upper cavity mold plate section 25 beyond the mold cavity30, as seen in FIG. 1.

As best seen in FIG. 2, the mandrel stack is supported on the cavitymold 24 with the mandrel teeth 40b extending into the mold cavity 30. Itwill be noted that only the distal ends of the mandrel teeth enter themold cavity 30 and that the free ends thereof are spaced from the cavityfloor. A plurality of leveling set screws 58 received in threaded bores58a in clamp blocks 48 bear against upper plate section 25 to level themandrel stack 22 relative to the cavity mold assembly 24. Once themandrel stack is leveled, a bolt 60 is passed through an elongated slot61 in a mounting bar 62 affixed to each clamp block 48 and threaded intoa tapped hole in the upper plate section 25 to rigidly secure themandrel stack to thecavity mold 24.

The casting apparatus of FIGS. 1 and 2 may be used to cast a spinneretteblank having any desired configuration by appropriate shaping of themold cavity 30. If it is desired that the cast spinnerette have acircular configuration, then the mold cavity should preferably also becircular. It becomes necessary to snap off those mandrel teeth 40b whichinterfere with the cavity mold 24 beyond the cavity 30. Alternatively,those mandrels 40 assembled adjacent to the clamp blocks 48 could beprovided with a lesser number of teeth than those near the center of themandrel stack 22.

Returning briefly to FIG. 3, the holes 40c in the backbone 40a of eachmandrel 40 are slightly asymmetrically arranged relative to themid-length center line thereof. Each mandrel is also provided with anedge notch 40d offset from the mid-length center line. If the mandrelsare assembled in the mandrel stack such that the notch 40d alternatesright and left of the mid-length center line, and the asymmetry of theholes 40c is such that the teeth of one mandrel are aligned with theteeth gaps in the adjacent mandrels, the spacing between rows of teethmay be reduced. By employing this assembly technique, a greater numberof holes may be formed in the spinnerette blank without weakening itsstructual integrity.

The preferred method by which a spinnerette blank is cast using theapparatus of FIGS. 1 and 2, and a finished spinnerette formed will nowbe described.

Once the cavity mold 24 is assembled, the recess 35 which accommodatesthe core 36 is filled with a fillet of a suitable adhesive sealant andthe core 36 is secured in place with bolts 37. This sealant prevents thecasting resin from seeping into the recess 35 and impeding removal ofthe cured casting from the cavity 30. If the core 36 is dispensed with,this operation is not necessary, except that the holes accommodatingbolts 37 must be sealed off. Prior to assembly of the mandrel stack 22,the mandrels 40 are cleaned with a suitable cleansing agent. After themandrel stack has been assembled, the mandrel teeth and thrust bars 54are given an application of a suitable mold release agent, as is thesurface of the cavity 30. Prior to mounting the mandrel stack atop thecavity mold 24, the thrust bars 54 are secured to the bottoms of thejack spacers 52 with rubber bands. This is preferred to laying thethrust bars across the cavity 30 as the risk of damaging the mandrelteeth during mounting the mandrel stack is lessened.

Once the mandrel stack 22 is mounted atop the cavi- -ty mold 24, it isleveled with set screws 58 (FIG. 2).

removed, freeing the thrust bars, and the various jack screws 520 areturned hand tight. The apparatus of FIGS. 1 and 2 is then ready forcasting.

The casting resin to which a suitable catalyst may be added is deaeratedin a vacuum. The casting resin is then poured into the pour hole 32 tofill the cavity 30. It is important that the cavity be filled to thepoint where the resin contacts the bottom surface of the thrust bars 54.This is necessary to insure a firm footing of the thrust bars on thecast spinnerette blank asthe mandrel stack is removed after the cure. Itshould be noted that the level of the casting resin 31 in cavity 30 isbelow the .casting apparatus is removed from the curing oven and thebolts 60 are removed. The various jack screws are turned hand tight andthen are each tightened about one quarter .to one-half a turn inrepeating sequence. The tightening program for the jack screws should besuch as to maintain the mandrel stack 22 substantially level orhorizontal at all times as it is separated from the cavity mold 24. Itwill beappreciated that excessive tipping of the mandrel stack canresult in bending of the mandrel teeth and damage to the hole patternproduced in a subsequently cast spinnerette blank. When the mandrelstack is completely withdrawn from the cast spinnerette blank, aplurality of blind holes are left therein by the mandrel teeth. Theconfiguration of each hole is in conformity with the cross-section ofthe mandrel tooth forming it. Withdrawal of the mandrel stack ispreferably effected while the casting is still near the curingtemperature and thus before any post cure shrinkage sets in.

The bolts 28 are then removed and the plate sections 25, 26 and 27 ofthe cavity mold assembly 24 are separated to extract the castspinnerette blank.

At this point it is preferable to subject the cast spinnerette blank toa second cure at a temperature somewhat higher than that of the initialcure. This second cure appears to develop the full flexural strength ofthe resin. Sudden cooling of the cast spinnerette blank after theinitial or the second tempering cure should be avoided to prevent thedevelopment of internal stresses.

The cast spinnerette blank must now be machined to the configuration anddimensions of a finished spinnerette. Before this is done, however, theblind holes in the blank left by the mandrel teeth should be filled withgrout to support the hole edges and to prevent resin chips from beingforced into the holes during machining. Suitable grouting materials aregelatin, Woods metal, para-dichloro benzene and water glass. It has beenfound desirable to degrease the spinnerette blank with methyl chloroformor trichloroethylene to facilitate the application of the groutingmaterial. The grouting material may be applied in a vacuum desiccator.

Machining of the spinnerette blank entails turning to a finisheddiameter, turning of the front and back faces, and finish grinding ofthe two faces. At the conclusion of the machining operation, the holesleft by the mandrel teeth extend from the front to the back faces of thespinnerette. The grouting material is then removed by any suitable meanssuch as an ultrasonic water bath. The addition of a suitable solvent inthe ultrasonic water bath facilitates grout removal. The finishedspinnerette 70 is in the form shown in FIG. 6. The holes formed by themandrel teeth are now spinnerette orifices 71 each of a shape conformingto the cross-see tion of the mandrel teeth.

In order to provide spinnerette 70 with added structual strength and toadapt it for mounting to an extrusion head, an annular mounting flange72 and crisscrossing reinforcing ribs 74 are bonded to it. Preferably,the annular flange 72 and reinforcing ribs 74 are formed and bonded tothe spinnerette 70 in a second casting apparatus (not shown). Thespinnerette 70 is placed in the bottom of a mold cavity and awaffle-like core is placed over it to cover the spinnerette orifices 71located between the reinforcing ribs 74 to be formed. The casting resin,which may be the same as that used in the formation of the spinnerette70, is introduced into the mold cavity and the casting apparatus placedin a vacuum for several minutes. The vacuum is then broken, and theresin is forced into the spinnerette orifices 71 left uncovered by thecore, thus insuring a strong bond between the mounting flange 72 andreinforcing ribs 74 and the spinnerette plate 70.

The cast spinnerette assembly is then cured and the mounting flange 72and reinforcing ribs 74 are machined, as required. Typically the onlymachining required is that of turning the spinnerette assembly to finishoff the annular mounting flange 72 to the desired final dimensions.

Rather than forming the annular mounting flange 72 and reinforcing ribs74 and bonding them to the spinnerette 70 in a separate castingapparatus, it will be appreciated that all three components may be castsimultaneously in a single casting apparatus to form a unitary assembly.However, machining becomes somewhat more complex.

The casting apparatus of FIGS. 1 and 2 is adapted to the formationcircular spinnerettes 70 (FIG. 6), as has been described. Withappropriate modifications, exemplified in the casting apparatus of FIGS.8 and 9, annular spinnerettes may be cast. The above described method ofmaking spinnerettes using the apparatus in FIGS. 1 and 2 is equallyapplicable to the production of annular spinnerettes.

Referring now to FIGS. 8 and 9, the spinnerette casting apparatus,generally indicated at 20', includes a mandrel stack assembly, generallyindicated at 22', supported on a cavity mold assembly generallyindicated at 24'. The assembly 24 includes an upper plate section 80 anda lower plate section 81, which are secured together by suitable meanssuch as bolts (not shown). The upper plate section 80 is machined so asto provide an annular mold cavity 82. An elongated groove 83 in theupper surface of plate section 81 extends between the mold cavity 82 anda pour hole 84 in plate section 80 to accommodate pouring the mold.

The mandrel stack 22, seen in both FIGS. 8 and 9, includes a head block86 in which is formed an annular channel 87. A pair of annular flanges88 and 89 extend into the channel 87 from its sidewalls. A peripheralarray of jack screws 90 together with a centrally disposed larger jackscrew 91 are threaded through the head block 86 of the mandrel stack 22and into abutting engagement with the upper surface of plate sectionwhen the mandrel stack is positioned atop the cavity mold assembly 24'.

Mandrels 92, best seen in FIGS. 8 and 10, like the mandrel 40 in FIG. 3are comb-like structures having a backbone or mounting strip 92asupporting a plurality of teeth 92b. Instead of aligning and assemblingholes, the mandrels 92 have a notch 920 formed in each vertical edge ofthe backbone 92a. As best seen in FIG. 8, the mandrels 92 are introducedinto the channel 87 in the mandrel stack head block 86 with the flanges88 and 89 engaging the mandrel notches 920, thus retaining them in themandrel stack 22'. As seen in FIG. 9, a keyway slot 94 is formed in themandrel stack head block 88. The inner end of slot 94 opens into theannular channel 87. A plug 97, accommodated in keyway slot 94, is movedto the closed end thereof such that the mandrels 92 may be introducedinto the channel 87 by way of the slot.

In addition to the mandrels 92, full mandrel spacers 95 are also loadedinto the mandrel stack 22'. The full mandrel spacers 95, seen in FIG.11, are provided with notches 95a which are engaged by the annularflanges 88 and 89 in the channel 87, thus also retaining them in themandrel stack. As in the apparatus of FIGS. 1 and 2, the mandrel stack22' is loaded such that the full mandrel spacers 95 are interposedbetween adjacent mandrels 92.

In order to take up the additional distance around the outercircumference of the channel 87 and to maintain the mandrels 92substantially radially aligned in the mandrel stack 22', half spacers96, best seen in FIG. 12, are also loaded into the channel 87. The halfspacers 96 are formed having a single notch 96a which is engaged by theouter annular flange 88 in channel 87. A small tooth 96b, carried by thehalf spacers 96, is received in an annular groove 88a formed in outerflange 88 (FIG. 8) to retain the half spacers in the channel.

A typical loading pattern would be a full mandrel spacer, a mandrel, afull mandrel spacer and then a half spacer 96 in repeating sequence.Periodically, additional half spacers 96 are inserted in order toachieve substantial radial alignment of the mandrels 92 in the mandrelstack 22.

After the mandrel stack 22' has been fully loaded, the plug 97 is pushedinwardly by advancement of a screw 98. A tongue 97a at the inner end ofplug is thus brought into engagement with the notches in the mandrelsand mandrel spacers in channel 87 opposite slot 94 to prevent them fromfalling out when the mandrel stack 22' is righted and placed atop thecavity mold Once the casting resin has been poured into the mold cavity82 and cured, the jack screws 90 and 91 are systematically tightened soas to withdraw the mandrel teeth 92a from the cast spinnerette blank enmasse while maintaining the mandrel stack 22' substantially level. Afterthe mandrel stack 22' is fully withdrawn,

the cavity mold assembly 24' is separated and the cast spinnerette blankis extracted. The blank is processed in the manner previously describedto form a finished annular spinnerette having orifices conforming insize and shape to the mandrel teeth 92a.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding descriptions, are efficiently attained and,since certain changes may be made in carrying out the above method andin the construction set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention, which, as amatter of language, might be said to fall therebetween.

Having described the invention, what is claimed as new and is desired tosecure by Letters Patent is:

1. A mandrel stack assembly for use as part of a casting apparatus forcasting spinnerette blanks comprising, in combination,

A. a plurality of comb-like mandrel units, each such mandrel unitcomprising a thin, substantially planar backbone to which are affixed aplurality of tooth-like core elements disposed in a single row along anedge of and in the same plane as said backbone, each of said toothlikecore elements having a maximum thickness identical to the thickness ofsaid thin, substantially planar backbone and being spaced from andsubstantially parallel to all the others of said tooth-like coreelements, said substantially planar backbone being less than about 0.04inches thick;

B. a plurality of spacer units, each such spacer unit comprising a thin,substantially planar member;

C. the backbones of said comb-like mandrels and the planar members ofsaid spacer units each being provided with means for mounting andaligning a plurality of said comb-like mandrels and said spacer units ina mandrel stack with the comb like teeth of said mandrels extendingfreely beyond the limits of said spacer units; and

D. means for securing together as a stack assembly said plurality ofcomb-like mandrel units and said plurality of spacer units;

B. said stack assembly having at least one such spacer unit disposedbetween the backbones of adjacent comb-like mandrel units.

2. A mandrel stack assembly as defined in claim 1 wherein said means formounting and aligning said comb-like mandrels and said spacer unitscomprises a plurality of holes therethrough and wherein said means forsecuring them together as a stack assembly comprises a pair of clampblocks and a plurality of clamp rods which pass through the aforesaidholes through said comb-like mandrels and said spacer units.

3. A mandrel stack assembly as defined in claim 2 including a jackmechanism comprising a jack spacer and a thrust bar, said jack spacercomprising an elongated bar provided with a plurality of holes throughwhich pass said plurality of clamp rods and a plurality of jack screwsextending transversely through said elongated bar parallel to saidtooth-like core elements, said thrust bar being immediately adjacentsaid jack spacer in contact wih the ends of id 'ack rews s id 'ackmechanism serving to wii hdr'tw 881 tooth-like ore elements from a castspinnerette blank when said jack screws are tightened against saidthrust bar which presses against said cast blank.

4. A mandrel stack assembly as defined in claim 1 wherein said means formounting and aligning said comb-like mandrels and said spacer unitscomprises notches in the backbones of said comb-like mandrels and insaid spacer units and wherein said means for securing them together as astack assembly comprises a head block provided with an annular channelof dimensions corresponding to the dimensions of the backbones of saidcomb-like mandrels and of said spacer units, said head block beingprovided with annular flanges within said annular channel located anddimensioned to fit within said notches when said comblike mandrels andsaid spacer units are located in said head block.

5. A mandrel stack assembly as defined in claim 4 also including aplurality of half spacers disposed within said annular channel adjacentthe larger circumference thereof.

6. A mandrel stack assembly as defined in claim 1 in combination with amold having a cavity into which a castable material can be introducedwherein said mandrel stack assembly is disposed so said tooth-like coreelements extend into said mold cavity.

7. A mandrel stack assembly as defined in claim 3 in combination with amold having a cavity into which a castable material can be introducedwherein said mandrel stack assembly is disposed so said tooth-like coreelements extend into said mold cavity and so a side of said thrust barremote from where said jack screws contact it forms a portion of themold cavity wall.

8. A mandrel stack assembly as defined in claim 4 in combination with amold having a generally annular cavity into which a castable materialcan be introduced wherein said mandrel stack assembly is disposed sosaid tooth-like core elements extend into said mold cavity.

9. A mandrel stack assembly in combination with a mold as defined inclaim 8 wherein said mandrel stack assembly is provided with a pluralityof jack screws extending therethrough parallel to said tooth-like coreelements, the ends of said jack screws bearing against said mold outsidesaid annular cavity.

1. A mandrel stack assembly for use as part of a casting apparatus forcasting spinnerette blanks comprising, in combination, A. a plurality ofcomb-like mandrel units, each such mandrel unit comprising a thin,substantially planar backbone to which are affixed a plurality oftooth-like core elements disposed in a single row along an edge of andin the same plane as said backbone, each of said tooth-like coreelements having a maximum thickness identical to the thickness of saidthin, substantially planar backbone and being spaced from andsubstantially parallel to all the others of said tooth-like coreelements, said substantially planar backbone being less than about 0.04inches thick; B. a plurality of spacer units, each such spacer unitcomprising a thin, substantially planar member; C. the backbones of saidcomb-like mandrels and the planar members of said spacer units eachbeing provided with means for mounting and aligning a plurality of saidcomb-like mandrels and said spacer units in a mandrel stack with thecomb-like teeth of said mandrels extending freely beyond the limits ofsaid spacer units; and D. means for securing together as a stackassembly said plurality of comb-like mandrel units and said plurality ofspacer units; E. said stack assembly having at least one such spacerunit disposed between the backbones of adjacent comb-like mandrel units.2. A mandrel stack assembly as defined in claim 1 wherein said means formounting and aligning said comb-like mandrels and said spacer unitscomprises a plurality of holes therethrough and wherein said means forsecuring them together as a stack assembly comprises a pair of clampblocks and a plurality of clamp rods which pass through the aforesaidholes through said comb-like mandrels and said spacer units.
 3. Amandrel stack assembly as defined in claim 2 including a jack mechanismcomprising a jack spacer and a thrust bar, said jack spacer comprisingan elongated bar provided with a plurality of holes through which passsaid plurality of clamp rods and a plurality of jack screws extendingtransversely through said elongated bar parallel to said tooth-like coreelements, said thrust bar being immediately adjacent said jack spacer incontact with the ends of said jack screws, said jack mechanism servingto withdraw said tooth-like core elements from a cast spinnerette blankwhen said jack screws are tightened against said thrust bar whichpresses against said cast blank.
 4. A mandrel stack assembly as definedin claim 1 wherein said means for mounting anD aligning said comb-likemandrels and said spacer units comprises notches in the backbones ofsaid comb-like mandrels and in said spacer units and wherein said meansfor securing them together as a stack assembly comprises a head blockprovided with an annular channel of dimensions corresponding to thedimensions of the backbones of said comb-like mandrels and of saidspacer units, said head block being provided with annular flanges withinsaid annular channel located and dimensioned to fit within said notcheswhen said comb-like mandrels and said spacer units are located in saidhead block.
 5. A mandrel stack assembly as defined in claim 4 alsoincluding a plurality of half spacers disposed within said annularchannel adjacent the larger circumference thereof.
 6. A mandrel stackassembly as defined in claim 1 in combination with a mold having acavity into which a castable material can be introduced wherein saidmandrel stack assembly is disposed so said tooth-like core elementsextend into said mold cavity.
 7. A mandrel stack assembly as defined inclaim 3 in combination with a mold having a cavity into which a castablematerial can be introduced wherein said mandrel stack assembly isdisposed so said tooth-like core elements extend into said mold cavityand so a side of said thrust bar remote from where said jack screwscontact it forms a portion of the mold cavity wall.
 8. A mandrel stackassembly as defined in claim 4 in combination with a mold having agenerally annular cavity into which a castable material can beintroduced wherein said mandrel stack assembly is disposed so saidtooth-like core elements extend into said mold cavity.
 9. A mandrelstack assembly in combination with a mold as defined in claim 8 whereinsaid mandrel stack assembly is provided with a plurality of jack screwsextending therethrough parallel to said tooth-like core elements, theends of said jack screws bearing against said mold outside said annularcavity.